Hi Sam, This acceleration limitation is by design, so that the TP can deal with tangential and normal acceleration separately. On a circular arc segment, the acceleration along the path is limited to 0.5 * a_max. Using the pythagorean theorem, the maximum normal acceleration is:
sqrt( a_max^2 - (1/2*a_max) ^2 ) = sqrt(3/2) * a_max ~= .866 * a_max So, if your maximum axis acceleration is 30 in/sec^2, then the TP only moves fast enough around the arc to create 25.98 in/sec^2 of normal acceleration. This way, if you have to speed up or slow down during an arc move, the total acceleration it won't exceed the machine maximum. A good analogy is high-speed cornering with a car on a twisty road. There's a maximum speed you can go around the corner before the tires slip. However, if you actually drive at that speed and have to hit the brakes, you're in trouble :). So, to be safe, you go a little slower so that you can slow down if need be. The good news is, this particular limit on tangential vs. cornering acceleration gets you pretty close to top speed. For example, on a 0.1" radius, a max normal acceleration of 26 in/sec^2 gives you a max speed of sqrt( 26 in/sec^2 * 0.1 in) ~= 1.61 in/sec. Compare that to 30 in/sec^2, which gives you sqrt( 30 in/sec^2 * 0.1 in) ~= 1.73 in/sec (about 7% difference). I just hard-coded this because it seemed to give me the best speed on my test runs. Maybe it could be an INI parameter? You could potentially get a little performance from a program with lots of circular arcs by reducing the tangential acceleration in favor of normal acceleration. Conversely, making tangential and normal acceleration both sqrt(2) * a_max might move more quickly in programs with a lot of detail like stellabee1.ngc. -Rob On Mon, Mar 24, 2014 at 2:47 PM, sam sokolik <sa...@empirescreen.com> wrote: > I have a question about the acceleration limits. (and I might be > nit-picking here) But I have been goofing around with the > trochoidal.ngc file from http://www.vagrearg.org/gcmc/trochoidal.ngc.gz > > I see when I push the velocity up to 3500mm/min - the peak velocity > starts to dip (this is with 30in/s^2 acc) > > http://imagebin.org/301375 > > but you can see that the acc doesn't get to 30in/s^2 - it seems to peak > at about 26 or so. I did play around with the gap freq in the ini file > (setting it to my servo period of 1000) and it may have helped just a > little bit. > > http://imagebin.org/301376 (acc peaks just a little higher) > > is this just a limitation of the whole system? It it still way way > better than the current tp - but was wondering what was causing this. > > sam > > ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/13534_NeoTech _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
